Props, especially for use in coal mines



B. TEBB ETAL PROPS, ESPECIALLY FOR USE IN COAL MINES July 21, 1959 3Sheets-Sheet 1 Filed June 8, 1956 IL 1 L? Inventor:

BERNARD TE-5B 0 w m W W A r. R w m M. A a

. July 21, 1,959 I B. TEBB ETAL 2,895,454

PROPS, ESPECIALLY FOR USE IN COAL MINES Filed Jun 8, l956 3 Sheets-Sheet2 I Inven for, 4 /91?!) T565 ERBEIFT PERKY 85/? CMKENIE W; T 2 x- Attore 31,6

2,895,454 PROPS, ESPECIALLY non USE IN COAL MINES Bernard Tebb,Swanland,

Hull, England, assignors ment Company Limited, company Application June8, 1956, Serial No. 590,185 Claims priority, application Great BritainJune 10, 1955 14 Claims. (Cl. 121-40) and Clarence Herbert Perry, toMastabar Mining Equip- Hull, England, a British The present inventionconcerns hydraulic pit props for mine roof supporting or shoringpurposes.

An object of the invention is to provide a prop of generally improvedstructure and performance which is especially suitable for filling therequirements in coal mines where, for example, a controlled roofcollapse may be necessary.

Another object is to provide for effecting collapse of the hydraulic pitprop from a safe distance. i

A further object is to enable the collapsing pressure to be selected byan external adjustment on the prop.

To achieve the first of these objects the present invention provides ahydraulic prop having a rising characteristic as regards its loadreleasing behaviour. Suoh rising characteristic implies that an initialrelease will take place on the attainment of a minimum predeterminedloading and that the loading to cause subsequent releases will increasewith load displacement until the value of theload becomes equal to themaximumload sustaining capacity of the prop.

Frictional or mechanical props, which may be at a disadvantage comparedWith hydraulic props on account of greater weight or fire hazard, haveindeed been constructed with rising characteristics; whereas hydraulicprops have hitherto allowed release of the load at a substantiallyconstant liquid pressure irrespective of load displacement, thus havinga flat characteristic.

T According to the present invention therefore a rising characteristichydraulic prop incorporates a liquid pressure relief valve adapted toopen at a varaible pressure and a relief pressure adjuster actuatedresponsive to a function of load displacement. The adjuster preferablyacts on the relief valve spring and may constitute or provide adisplaceable spring adjustment or anchorage.

Thus the relief valve on a first portion of the prop may be urgedtowards its seat by a spring, for example in theform of a torsion baranchored on the fulcrum of a lever constituting the adjuster, a secondportion of the prop displaceable relative to the firstporti'on carryinga cam adapted on displacement occurring to swing the lever and therebyefiect rotation of the anchor end of the swing.

Instead of the adjuster being moved mechanically responsive todisplacement it may be displaced hydraulically, for example,constituting part of a chamber of variable volume which is expanded byadmission thereto of liquid discharged past the relief valve itself.

According to a further feature of the invention a torsion spring loadinga relief valve or valves is anchored to a spring loaded memberpresenting an attachment for an external operating element such as alanyard. Then on displacement of the member against its spring loadingthe relief valve loading may be reduced, so as to initiate collapse ofthe prop.

The position of the spring loading member is preferably adjustable, i.e.by a screwed stop or collar so as toenable the loading of thetorsionspring on the relief valve and hence the normal collapsing load to bevaried.

The torsion spring may provide positive loading for one relief valve andsecondary loading for a second relief valve.

The invention will be described further with reference to theaccompanying drawings in which:

Fig. 1 is a medial vertical section of a hydraulic pit, prop constructedin accordance with the invention;

Fig. 2 is an elevation of the adjustable release control shown in Fig. 1

Fig. 3 is an enlarged fragmentary horizontal section on the lineIlI--III of Fig. 1;

Fig. 4 is a part medial vertical section of a portion of an alternativeform of hydraulic pit prop constructed in accordance with the invention;

Fig. 5 is a medial vertical section of a modification of the prop shownin Fig. 4;

Fig. 6 is a medial vertical section showing a further form ofhydraulicpit prop in accordance with the invention; i

Fig. 7 is a horizontal section on the line VIIVH of H Fig. 6; and

' Fig. 8 is a horizontal cross section on the line VIII- VIII of Fig. 6certain parts being similar to those shown in Fig. 3.

In the drawings like reference numerals refer to like 1 parts.

In the prop shown in Figs. 1 to 3, embodying a mechanically displacedadjuster, an upper or first portion 11 includes a hollow piston or ram12 attached at its lower end and received Within a cylinder forming thelower or second prop portion 14 fixed to the'base 15 of the prop. Theupper telescopic member 11 is secured at its upper end by way of acollar 16 to an upper extension 17 which, at its upper end, is fixed tothe head 18 of the prop.

The inverted piston head 12 includes a chamber 43 formed therewithin bya screwed plug 44 engaged in a threaded and counterbored inverted borein the piston 12. The plug 44 is provided with an oil sealing or packingring 4411, and its lower end is flanged so as to engage and retain anend plate 45 which serves: to retain an oil seal 13.. The chamber 43communicates with the interior. of the upper telescopic member 11 whichconstitutes an oil reservoir, by way of a bore 47. A space 50, below thepiston 12, within the telescopic member 14 communicates with the chamber43 by way of a vertical bore 55 which runs into a horizontal bore 56. Aball relief valve "57, displaceable within the bore 56 is adapted, inits closed position, to prevent entry of oil from the space 50 to thechamber 43.

The ball 57 is urged towards its seating 58 by a pres sure bar 62projecting radially from near the lower end of a vertically extendingspring torsion bar 61 suitably guided at or near both its ends forrotary movement relative to the piston 12. The upper end of the torsionbar 61 is attachedat one end of an arm 64 and thus by reason of itsguiding this end of the bar 61 with the arm 64 constitutes a leverfulcrum. The other end of the arm 64 projects outwardly through a slot80 in the wall of the upper extension 17 of the upper prop to permit ofadjustment of the initial spring pressure.

An inlet connection (not shown) is provided to the space 50, thus withany suitable preloading of the prop in its initial or maximum heightcondition, liquid may be pumped into this space 50 of the cylinder.

In the alternative form of construction shown in Fig. 4

hydraulic displacement of the adjuster is efiected by making theadjuster in the form of a floating piston 81 displaceable within thepiston skirt or hollow cylindrical part of. the upper portion 11 of theprop. This. floating piston -81 then forms the upper wall of a chamber82 of variable volume constituted by the space within the lower .part ofthe upper portion of the prop, i.e. between the floating piston 81 andthe upper surface of the inverted head of the prop piston 12. A reliefvalve 83 is arranged to discharge liquid into the variable volumechamber 82 with the result that the floating piston 81 is moved upwardlyrelative to the piston head- '12. The relief valve 83 is disposed withinthe piston headI 12. and is adapted to move downwardly to open and isloadedby a coiled tension spring 84 anchored at its upper end' to thefloating piston 81. Thusafter discharge of. liquid from the relief valve83 the floating piston 81 rises and: increased tensional spring.pressure is applied to the valve 83.

Alternatively, as shown in Fig. 5, a coiled compression spring 85 iscontained in the space 86 between the-upper, most interior part of theupper portion of theprop and. the floating piston 81, its lower endresting on an abutment 87 which bears downwardly on an upwardly openingrelief valve 83 in the. floating piston 81. This valve 83 is connectedto a passage 88 through the propwpiston head 12 by way of a highpressure coiled flexible con duit 89. Hence on liquid being dischargedby the valve 83, downwardly into the chamber 82 below the floatingpiston 81, the floating piston 81 rises carrying the relief valve 83with it. This upward displacement. of the floating piston 81 or adjusterprovides a relative displacement of the abutment 87 of the upper end ofthe coiled compression spring 85 which is thereby compressed so astoincrease the pressure exerted on the relief valve 83.

In both these hydraulic arrangements at low pressure subsidiary reliefvalve 90 discharging upwardly is provided to relieve excessive pressuredeveloping below the floating piston 81. External connections both tothe prop, or high pressure cylinder and to the chamber of variablevolume or low pressure cylinder are provided.

to enable the prop to be appropriately preloadedon its. initialinstallation. I t

In the embodiment shown in Figs. 6 to 8,, a hydraulic pit prop includesan upper telescopic member 11 having a piston 12 attached to its lowerend. The piston carriesa sealing ring 13 adapted to seal the piston inliquid tight manner within a cylinder constituted by. a lower telescopicmember 14 fixed to the base 15 of the prop.

The upper telescopic member is secured at its upper end: by way of acollar 16 to an upper extension 17 which at its upper end is fixed tothe head 18 of the prop.

A pump cylinder 21 is fixed in a screwed bore. atthe topof the piston12. In this cylinder a large piston 22.

is displaceable. The large piston -22 is axiallybored to."

accommodate a piston rod 23 and counterbored to form. a smaller diameterpump cylinder 24 within which-a small piston 25 fixed to the lower endof the'piston rod 23 is displaceable. The upper end of the piston rod isfixed in. av clevis 26 which is urge-d upwardly relative to the largepump piston 22 by a coiled compression spring 27. A connecting rod 28 ispivoted. at its lower end to the clevis by means of a pin 29, and itsupper end. is pivotally connected to a crank 30 adapted to-berotated byapplication of a suitable hand tool to the squared outer end 31. of itsshaft 32 whichisjournall'edvina socket 33 secured in the wall oftlreextension: 17. Suitable oil sealing or pacldng ringsare provided/onthe pump-pistons 22 and 25-and on the 'pump' crankshaft 32.

The working space of the pump cylinders corn'munia cates by Way of aninlet ball valve-"41' and abore' 42' with an enclosed chamber 43*formedwithin thefp'rop the upper telescopic member 11 which constitutes an oilreservoir, by way of a bore 47. The Working space of the pump pistonscommunicates by way of a bore 48, the outlet valve 46 and an aperture 49in the plate 45 with a space 50, below the piston 12, within the lowertelescopic'member 14.

The space 50 communicates with the chamber 43 by way of a vertical bore51 which runs into a horizontal bore 52. A release valve 53 is urged onto a seating, which results from a change in diameter of bore 52, by acoiled compression spring 54. Space 50 further communicates with thechamber 43 by way of a vertical bore 55 which runs into a horizontalbore 56. A relief valve. 57 slidable within bore 56, is urged against aseating 58 within bore-56 by means of a-vertically extending torsion barspring 61 which passes downwardly through.

striker 63 adapted to bear against the valve 53 on rotation of torsionbar spring 61.

The. upper end of the torsion spring is fixed to an arm 64 which ispivotally connected to a link 65 which. in

turn is pivotally connected to a lug 66 of a plunger 67. This plunger isdisplaceable in a cylindrical housing 68 containing a spring69 whichbears against an adjustable abutment plug 70 and urges the plunger inaninward direction. The shank of the plunger passes outwardly through abore in the plug 70 and is screwed into an eye 71. A lanyard foreffecting release of the prop may be passed through the aperture in theeye 71; or alternatively, as shown a rod 72 is fitted into this apertureand arranged to engage a wedge ended cam or release bar 73. This bar 73is adjustable in a vertical direction relative to the lower telescopicprop member 14 by means of a clamp 74 so as to enable the cam profile tocause outward displacement of the plunger to a required extent in agiven relative position of the two telescopic members 11 and 14 of theprop.

In operation the prop is extended by manually imparting rotation to theshaft 31 using an appropriate brace or other tool engaged on the squaredend of this shaft. Rotation of the shaft 31 causes the crank 30 toimpart vertical small piston 25. This results in a rapid displacement ofoil from the reservoir, through the bore 47 into chamber 43' and throughthe bore 42- and past valve 41 into the pump cylinder 21 and thencethrough the bore 48, past vaiCe 46 and through the aperture 49 into thespace 50,

with the result that the upper member 11 is forced outwardl'y', therebyextending the prop. When, however, the head 18 bears against the mineroof the pressure within the space rises rapidly and further rotation ofthe shaft 31 causes the small piston 25 to move relative to the largepiston 22 as soon as the upward thrust due to liquid pressure on thelarge piston 22 exceeds the downward thrust exerted upon it by thespring, 27. Continued pumping action is then efiected by reciprocationof the small piston 25 which thus enables a preloading pressure to beapplied with relatively small liquid displacement to the space 50 andthereby to the prop as a whole.

Torsion bar spring 61 is initially adjusted to main.-

' tain valve 57 against seating 58 by means of adjustable plug 7 0;Excessive pressure within sp'ace50 unseats valve 57 and oil flows fromspace 50 to the reservoir via bores 55, 56, chamber 43 and bore 47causing collapse of the prop (or less rapid extension). The unseating ofvalve 57 is assisted by outward movement of plunger 67 causing rotationof torsion bar spring 61 and arm 62. Further outward movement of plunger67 causes striker 63 to unseat valve 53 and oil flowing from space 50 tothe reservoir is provided with an additional path via bores 51, 52,chamber 43 and bore 47.

Outward movement of plunger 67 is elfeoted by pulling on the eye 71 bymeans of a lanyard or other external operating element or is effectedautomatically during extension of the prop by means of the wedge endedcam 73. It will be appreciated that the Wedge ended cam will also causeinward movement of plunger 67 during collapse of the prop, thusprogressively increasing the resistance of the prop to collapse.

We claim:

1. In a hydraulically extensible pit prop having a risingcharacteristic, hydraulic load sustaining means, pressure relief meansadapted on opening to relieve hydraulic pressure within said loadsustaining means, and relief pressure adjusting means bearing on saidpressure relief means and defining a range of relief pressures at whichsaid pressure relief means is permitted to open, said adjusting meansbeing operable responsive to a function of load displacement to rendersaid relief pressure continuously variable within said range duringextension and contraction of said prop.

2. A hydraulically extensible pit prop comprising an upper telescopicmember, a lower telescopic member, one of said members acting as apiston and being displaceable in a hydraulic cylinder constituted by theother of said members, a liquid pressure relief valve communicating withsaid cylinder and adapted to open to relieve hydraulic pressure therein,and relief pressure adjusting means bearing on said relief valve anddefining a range of relief pressures at which said valve is permitted toopen, said adjusting means being operable responsive to a function ofload displacement to render said relief pressure continuously variablewithin said range during relative move ment between said telescopicmembers.

3. In a hydraulically extensible pit prop having first and secondrelatively displaceable portions, a relief valve on said first portion,spring means for urging said relief valve into its closed condition, anadjusting means carried by said first portion and constituting adisplaceable anchorage for said spring means, and cam means on saidsecond portion adapted to displace said adjusting means and thereby varythe pressure exerted by said spring means on said relief valveresponsive to the relative positions of said first and second portions.

4. In a hydraulically extensible pit prop having first and secondrelatively displaceable portions, a relief valve on said first portion,a torsion bar spring for urging said relief valve into its closedcondition, a lever carried by said first portion and connected at itsfulcrum to said torsion bar spring so as to constitute a displaceableanchorage for said spring, and cam means on said second portion adaptedto displace said lever and thereby vary the pressure exerted by saidtorsion bar spring on said relief valve responsive to the relativepositions of said first and second portions.

4. In a hydraulically extensible pit prop having first and secondrelatively displaceable portions, a relief valve on said first portion,a torsion bar spring for urging said relief valve into its closedcondition, a lever carried by said first portion and connected at itsfulcrum to said torsion bar spring so as to constitute a displaceableanchorage for said spring, and cam means on said second portion adaptedto displace said lever and thereby vary the pressure exerted by saidtorsion bar spring on said relief valve responsive to the relativepositions of said first and second portions.

. In a hydraulically extensible pit prop having first and secondrelatively displaceable portions, a relief valve on said first portion,spring means for urging said relief valve into its closed condition, adisplaceable wall in said first portion defining therein a chamber ofvariable volume, said wall being displaced in accordance with the amountof liquid contained in said chamber and constituting a displaceableanchorage for said spring means, and conduit means for feeding hydraulicliquid discharged by said relief valve into said chamber to thereby varythe pressure exerted on the relief valve by said spring means responsiveto the relative positions of said first and second portions.

6. In a hydraulically extensible pit prop formed with a reservoir forhydraulic fluid and a working chamber into which said fluid is intendedto be urged under pressure to extend said prop, a torsion bar spring, atleast one fluid pressure controlling valve communicating with saidworking chamber loaded by means of said torsion bar spring, said valvecontrolling the discharge of pressure fluid from said working chamber, aspring loaded displaceable member to which said torsion bar spring isanchored, means acting on said displaceable member for displacing saidmember between fixed limits during extension and contraction of saidprop, the displacement of said member thereby varying between upper andlower limits, the load exerted by said torsion spring on saidcontrolling valve, and an external operating means attached externallyto said spring loaded displaceable member and by which said member isdisplaced to cause the load exerted on the valve by the torsion barspring to be removed for collapse of the prop.

7. A structure according to claim 6, in which said spring-loaded memberis adjustable.

8. A structure according to claim 6, in which said spring-loaded memberis adjustable by means of a screwed stop.

9. A structure according to claim 6 in which the fluid pressure controlvalve is a pressure relief valve, and said structure further comprisesat least one further relief valve, the torsion bar spring providingpositive loading for one relief valve, and negative loading for theother relief valve.

10. In a hydraulically extensible pit prop having an upper portion and alower portion, said upper portion being formed with a chamberconstituting a reservoir for hydraulic fluid and said lower portionbeing formed with a chamber constituting a work chamber into whichhydraulic fluid is intended to be urged to extend the prop, a pistondisplaceable in the chamber presented by said lower prop portion, arelief valve carried by said piston and controlling communicationbetween said lower chamber and that presented by the upper prop portion,a vertically extending torsion bar spring having an upper end and alower end, guide means adjacent to and guiding said ends for rotation ofsaid torsion bar spring relative to said upper prop portion, means foradjustably anchoring the upper end of said spring against rotationrelative to said upper prop portion, and an arm fixed to said spring atthe lower end thereof and adapted to transmit the spring pressure tosaid valve to urge it towards its closed condition in opposition to thefluid pressure in the lower chamber.

11. A structure according to claim 10 including a second arm fixed tothe upper end of the spring perpendicularly thereto, the upper propportion being slotted to permit said second arm to extend horizontallyoutwardly therethrough, and a cam-bar carried by the lower prop portionand adapted to bear on said second arm and vary its angular positionrelative to the prop in accordance with the relative positions of saidupper and lower prop portions.

12. In a hydraulically extensible pit prop having two relativelydisplaceable portions, a hydraulic pressure relief valve carried by oneof said portions, a torsion spring loading said valve, an anchoragemember connected to said spring and displaceably mounted on said portioncarrying the relief valve, an external operating member for displacement'of said anchorage member and an attachment for said external operatingmember whereby said valve may be caused to open by displacement of saidanchorage member and consequential variation in the loading applied tosaid valve by said torsion spring.

13-. In a hydraulically extensible pit prop having a continuously.varying rising characteristic as regards its load releasing behaviour,hydraulic load sustaining means, pressure relief means adapted onopening to relieve hydraulic pressure within said load sustaining means,and hydraulically displaced relief pressure adjusting means for varyingthe hydraulic pressure at which said relief means opens responsive to afunction of the amount of hydraulic liquid discharged by said reliefmeans.

14. A hydraulically extensible pit prop comprising an upper telescopicmember, a lower telescopic member, one

of saidmembers acting as a piston and being displaceable in a hydrauliccylinder constituted by the other of said members, a liquid pressurerelief valve communicating with said cylinder and adapted to open at avariable pressure, and hydraulically displaced relief pressure adjustingmeans acting on said relief valve responsive to a function of the amountof hydraulic liquid discharged by said valve whereby to provide a risingcharacteristic in the load-displacement behaviour of the prop.

References Cited in the file ofthis patent UNITED STATES PATENTS2,618,122 Gratzmuller Nov. 18, 1952 2,621,631 Dowty ,Dec. 11, 19522,638,075 Towler May 12, 1953 2,699,180 Frye Jan. 11, 1955 2,713,773Sutton July 26, 1955

